Method and apparatus for sheet and carton blank aligning

ABSTRACT

Apparatus and a method aligns and orients a moving article, such as a sheet or a carton blank during processing of the sheet/carton blank, relative to its intended path of travel through a conveyor-type assembly machine. In one embodiment, a pair of sensors detect passage of respective laterally spaced leading edge portions of the moving sheet and provide inputs to a controller which, in turn, provides an appropriate signal to one of a pair of spaced sheet-gripping rollers in contact with the respective laterally spaced portions of the sheet for aligning, or squaring, the sheet&#39;s leading edge relative to its intended path through the assembly machine. In another embodiment, a single sensor detects a linear lateral edge of the sheet and a single drive element orients and aligns the sheet&#39;s edge so that it is coincident with and parallel to a linear target line defining the intended path of travel.

RELATED APPLICATION

This application claims priority pursuant to 35 U.S.C. 119(e) from U.S. Provisional Application Ser. No. 61/581,505 filed Dec. 29, 2011.

FIELD OF THE INVENTION

The present invention is directed to an improved apparatus and method for aligning sheets or folding carton blanks on a conveying system such as used in carton folder/gluers.

BACKGROUND OF THE INVENTION

In processes involving printing on sheets of material such as paper or processing folding carton blanks, it is typically desirable that in the case of a rectangular sheet or blank that the side edges are parallel to the conveying direction and/or the leading edge is perpendicular to the conveying direction. This allows operations such as printing to be properly oriented with respect to the sheet or blank. In carton folding/gluing operations, flat sheets/carton blanks are folded along score lines and glued along a seam or at a corner, or corners, to provide a carton ready for subsequent uses such as erecting or filling. Carton folder/gluers typically include a feeder which dispenses a flat, die cut carton blank from the bottom of a stack of blanks. These feeders often do not dispense a carton blank with the desired orientation alignment because of many factors including asymmetry of carton shape and uneven weight distribution in the feeder, varying feeder belt friction coefficients, differences in feed gate settings, and other factors. Immediately after leaving the feeder, cartons are gripped by carrier belts. To create a desired spacing between each carton blank on the carrier belts, the carrier belts run faster than the feeder belts. This creates a brief ‘tug of war’ while the carton is released by the slower moving feeder belts and engaged by the faster moving carrier belts. The feeder and carrier belt positioning is often asymmetric with respect to the carton and this can cause a carton blank to twist out of the desired orientation.

Folder/gluer operators strive to make cartons feed “square,” or “aligned”, i.e., in the desired orientation with respect to the conveying direction on the carrier belts. This requires a high degree of operator skill based on years of experience.

To reduce the level of operator skill required and to better assure proper orientation regardless of machine parameters that often vary during operation, carton folder/gluers often include a carton aligner, or aligning section. In prior art aligning processes, the sheets or carton blanks have been conveyed by carrier belts with overlying balls or rollers that lightly grip the sheet or blank and laterally urge the sheet or blank against a mechanical guide comprised of an adjustable sheet metal plate with a smooth, flat surface. This section of the machinery is known as an aligning section. The loose contact between belts and angled rollers allows the sheet to shift so that it can become aligned with respect to the alignment guide bar which typically sets a side edge of a blank parallel with subsequent lower carrier belts and upper gripping belts, or rollers. This is intended to desirably align the sheet or blank for subsequent operations. Aligning sections having this general configuration are sold in Signature™ folder gluers sold by American International Machinery of Oak Creek, Wis. and folder gluers made by Bobst Group SA of Lausanne, Switzerland, and others.

As another example, U.S. Pat. No. 6,162,157 to Morisod shows an alignment device that, while using a traditional guide bar 100, uses air flow to lightly contact blanks of “low specific gravity”, partly folded blanks and other delicate blanks against an angled belt which otherwise traditionally directs the blank against the guide bar.

There are some drawbacks to the prior art method of aligning flat sheets or carton blanks including:

-   -   There is typically no feedback to sense and confirm sheet or         carton alignment after going through the aligning section.     -   Sometimes the side edges on a sheet or carton are relatively         short and/or irregular and thus are not effectively aligned in         prior art aligning sections.     -   Set up of the aligning section involves adjusting numerous         components and variables and requires an experienced operator.     -   The sheet or carton blank is not firmly gripped or controlled         during the aligning process. Thus, the speed and position of the         sheet or carton blank in the aligning section is not well         defined, repeatable, or predictable.

There are some subsequent processes such as applying adhesive with systems provided by Nordson of Westlake, Ohio, or windowing systems such as provided by Tamarack Products of Wauconda, Ill., that require the speed and position of the blank to be known so that subsequent speed and position can be accurately predicted. For example, the Tamarack® Vista® windowing machine uses a scanner approximately two feet ahead of the Vista windower to sense carton position. Carton speed is indirectly sensed by an encoder that measures the speed of a lower carrier belt. During aligning, substantial slippage occurs between the sheet or carton blank and the carrier belts in the aligning section, preventing proper sensing of sheet/carton speed and accurate prediction determination of the sheet/carton's subsequent position with the result that the window application position will not be accurate. For these applications, the sheet/carton blank must be sensed later in the process, after aligning. This necessitates scanning of the blank later in the folder/gluer and can result in an undesirable or impractical location for the windower unit.

SUMMARY OF THE INVENTION

The instant invention relates to a new method and apparatus for aligning sheets or folding carton blanks. Two laterally separated scanners each sense a respective portion of the lead edge of a blank. The signals from the scanners are fed to a processor which evaluates the timing difference (or the difference in master encoder or virtual master pulses) between each scanner's signal. Two sets of grippers engage each sheet or blank adjacent its side edges. The grippers are capable of operating at different speeds via a differential drive or electronically controlled servo drives. Differing speeds are commanded at each gripper in order to steer or rotate the blank relative to subsequent carrier belts. Suitable servo control systems for these steps of operation are manufactured by Bosch Rexroth of Lohr am Main in Germany.

The alignment of the blank can be adjusted in a over a shorter distance than prior art approaches and its average velocity can be adjusted to be very close to its velocity on subsequent carrier belts—allowing for a more compact folder/gluer and more freedom in locating a windower unit.

Steering the blank is no longer determined by a side edge of the blank riding against a mechanical guide, so side edge length and possible irregularities in the side edge are no longer a concern.

A non-rectangular sheet/blank can be aligned as desired and a leading edge with irregularities such as tabs, angles, or cut-out portions can all be accommodated to provide highly accurate sheet/blank positioning and orientation.

BRIEF SUMMARY OF THE DRAWINGS

The appended claims set forth those novel features which characterize the invention. However, the invention itself, as well as further objects and advantages thereof, will best be understood by reference to the following detailed description of a preferred embodiment taken in conjunction with the accompanying drawings, where like reference characters identify like elements throughout the various figures, in which:

FIGS. 1 a, 1 b, 1 c represent a progression of schematic top views of a prior art apparatus and method for aligning folding cartons;

FIG. 2 illustrates a schematic partial front view of a prior art apparatus;

FIG. 3 is an upper perspective simplified view of the inventive apparatus for sheet and carton blank aligning;

FIGS. 4 a, 4 b, 4 c, and 4 d illustrate a progression of top views of the inventive apparatus and method for squaring the lead edge of a carton blank;

FIG. 5 illustrates a simplified graphical user interface image for soliciting scanner and wheel positions used to program the inventive apparatus' control system;

FIG. 6 illustrates a schematic top view of a carton blank in two positions, where one position elicits a clockwise corrective motion as viewed in the figure from the inventive aligning system and the other position elicits a counter clockwise corrective motion;

FIG. 7 illustrates a schematic top plan view of a carton blank in four positions, where the first three positions represent a series of three incremental steps as part of an interative process for aligning the carton blank, and the fourth position represents a subsequent position, after the corrective process, where the carton is in the desired orientation and side edge alignment; and

FIG. 8 Illustrates a schematic top plan view of a typical carton blank for a graphical user interface and corresponding offsets needed to accommodate the carton blank's perimeter features.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 a and 1 b show a top view schematic of a prior art carton aligner used with prior art carton folder/gluers such as those provided by American International Machinery of Oak Creek, Wis., Bobst of Lausanne, Switzerland and Heidelberger Druckmaschinen AG of Heidelberg, Germany. Carton blank 11, shown here in a skewed orientation relative to its intended conveying direction D, is carried on driven carrier belt 12. Carrier belt 12 is typically driven by drive pulleys on a drive shaft via a motor drive system (not shown). In FIG. 1 a, side edge 11 a of blank 11 is about to contact alignment guide bar 13. Guide bar 13 is supported by side frame 16 a, by conventional means, which are not shown. Blank 11 is driven towards aligning surface 13 a of bar 13 by a series of rollers 17 that are attached to an adjustable frame 18 via pivot 14 and adjuster 15. The frame 18 is supported by side frame 16 a. The rollers 17 are shown in an angled orientation relative to side frames 16 a, 16 b and guide bar 13 such that the rollers develop a side force that urges blank 11 towards alignment bar 13 so that carton edge 11 a is urged into contact with alignment edge 13 a. Unlike carrier belt 12, rollers 17 are not directly driven. Rather, rollers 17 rotate by virtue of frictional contact with the carton blank 11 and if the blank is absent, by contact with carrier belt 12.

FIG. 1 b shows a subsequent moment in time in relation to FIG. 1 a. Carton blank 11 has moved to the left as viewed in FIG. 1 b, or downstream, and has rotated clockwise as a result of contact with guide bar 13 and the side force exerted by the skewed rollers 17.

FIG. 1 c illustrates a still later moment in time. Carton blank 11 has rotated further clockwise and has come into contact with aligning edge 13 a so that the carton blank is now traveling parallel to aligning edge 13 a, which is typically also parallel with side frames 16 a and 16 b. Edge 13 a defines the desired carton 11 conveying direction D. Edge 13 a also defines the lateral position of carton edge 11 a relative to side frames 16 a, 16 b so that subsequent operations, such as folding at various scores, window application, labeling, die cutting, and other operations known in the art (but not shown here), can be performed at the desired lateral locations on carton blank 11.

FIG. 2 is a side view schematic of the prior art apparatus of FIGS. 1 a-c. Carrier belt 12 is supported by rollers 19. Rollers 17 are spring loaded to grip the carton blank 11 and urge it into contact with carrier belt 12 disposed on rollers 19. The grip of the rollers 17 and belt 12 on the carton blank 11 is adjustable so that the blank is driven forward (to the left as shown in FIGS. 1 a-c and FIG. 2) in the folder/gluer reliably and also driven against the alignment bar 13, but not so tightly that the carton blank is deformed against the alignment bar by excessive lateral forces. Also, the carton blank 11 must be lightly enough gripped to allow the carton blank to rotate (relative to the plane illustrated in FIGS. 1 a-c) into the desired orientation with alignment edge 13 a. The requirements for positively driving the blank forward while allowing it to slip so it can be aligned are at cross-purposes and require skilled operator adjustment for a particular job. For more reliable performance, the alignment bar 13 and frame 18 with angled rollers 17 are quite long and an aligning module to support the aligning components typically adds about 3-4 ft to the length of an already long and sizable carton folder/gluer. While the carton blank 11 is in the alignment section, the twisting and slippage of the carton blank prevents its speed and position from being accurately defined or predictable. This can interfere with operations like in-line window affixing such as provided by the Vista window applicator of Tamarack Products Inc of Wauconda, Ill. which is the subject of U.S. Pat. Nos. 6,772,663 and 7,901,533, the disclosures of which are incorporated herein by reference.

FIG. 3 is an upper perspective view of a carton folder/gluer that includes an improved carton aligner 30 in accordance with one embodiment of the present invention. Some support structure for the components has been deleted to illustrate the inventive concepts more clearly. The main components of the carton aligner 30 are a vacuum belt module 31 which drives belts 35 a, 35 b, and 35 c (via a mechanical drive and motor, not shown) and its opposing gripper assembly, or roller, 32, powered upper gripper assembly, or drive roller, 33 and its opposing gripper assembly, or roller, 34, and scanners 36 a and 36 b. In the instant in time depicted in FIG. 3, carton blank 11 is conveyed by vacuum belt module 31 in the direction indicated by arrow D. In a subsequent time interval, carton blank 11 will be gripped between (i) belt 35 b and opposing gripper 32 and (ii) powered gripper 33 and opposing gripper 34.

Powered upper gripper assembly 33 can be driven in a variety of ways. In a preferred embodiment, a servo motor 33 m, such as provided by Bosch Rexroth of Lohr am Main, Germany drives gripper 33 directly. The servo motor 33 m is controlled precisely by a Bosch Rexroth control system and programmed with Visual Motion software also supplied by Bosch Rexroth, and programmed by the user. Additional disclosure of the servo control system is provided in the aforementioned references U.S. Pat. Nos. 6,772,663 and 7,901,533. To reduce cost, a stepper motor could be substituted, or a mechanical drive via belts, pulleys, gears, etc., from the folder/gluer drive could drive gripper 33 via a differential gearbox such as provided by Tandler of Bremen, Germany or Harmonic Drives of Peabody, Mass. Drive gripper 33 drives opposing roller 34 when carton blank 11 is not present therebetween. When carton blank 11 is gripped between drive roller 33 and opposing roller 34, drive roller 33 drives carton blank 11 and, in turn, carton blank 11 drives opposing roller 34.

In normal operation, i.e., when no corrective action is being performed on the orientation of carton blank 11, drive roller 33 and vacuum belt 35 b will have identical outer perimeter speeds and the carton blank 11 will be conveyed in the direction D and in the same orientation as it was received into engagement between gripper assembly 32 and drive belt 35 b and between gripper assembly 33 and gripper assembly 34.

Vacuum belt module 31 is driven by the machine drive (not shown), typically an AC or DC variable speed motor drive, as commanded by the operator's speed input to a graphical user interface such as provided by Exor of Torino, Italy or other known means of operator interface such as speed up/down pushbuttons or speed control dials. Opposing gripper assembly 32 is then driven by the vacuum belts when carton blank 11 is not gripped between belt 35 b and gripper assembly 32. When carton blank 11 is gripped between belt 35 b and gripper assembly 32, belt 35 b drives carton 11 and, in turn, carton 11 drives gripper assembly 32.

Scanners 36 a and 36 b, such as provided by Keyence of Osaka, Japan, are used to sense the position of the lead edge, or other scannable feature, of carton blank 11. Presuming that the lead edge of carton blank 11 is perpendicular to the desired direction of travel D, then scanners 36 a and 36 b will sense the carton blank's lead edge at the same time. If the carton blank 11 is skewed, scanners 36 a and 36 b will sense the leading edge at different points in time.

Signals from the scanners 36 a, 36 b are fed as inputs to a servo controller (not shown), such as a Bosch Rexroth PPC. In cases where the inventive carton aligner is used in conjunction with a Tamarack Vista window applicator, the PPC and graphical user interface, or touchscreen, will already be in place for the Vista windower and readily accepts these additional inputs. The general operation of the servo control system is disclosed in U.S. Pat. Nos. 6,772,663 and 7,901,533, already referenced. In a preferred embodiment, the scanners are located ahead of the gripper assemblies 32, 33, and 34. The advantage of this positioning is that the carton blank 11 will be firmly gripped by and under control of the gripper assemblies 32, 33, 34 and vacuum belt 35 b, assuring accurate control and performance of the aligning process.

In a simplified mode of operation, if scanners 36 a, 36 b sense the carton blank 11 lead edge at the same time, the blank 11 is aligned square with the direction of motion D and no corrective action is needed. The servo system commands the servo motor to rotate upper gripper assembly 33 so that its outer peripheral speed matches the speed of vacuum belt 35 b.

If scanner 36 a senses the carton lead edge before sensor 36 b, the time (or number of encoder pulses) difference is noted by the servo control system and the servo motor 33 m is commanded to temporarily slow down. This causes the carton blank 11 to rotate slightly clockwise when viewed from the top, swinging the carton into the desired alignment. The pivot points of the rotation will be located essentially under gripper assembly 32.

If the opposite case occurs, i.e., scanner 36 a senses the carton lead edge after sensor 36 b, then servo motor 33 m is temporarily commanded to speed up.

In a simplified embodiment as shown in FIGS. 4 a-d, scanner 36 b is in line with gripper assembly 32. Scanner 36 a is in line with servo-driven gripper assembly 33. Arrow 32 v represents the relative velocity vector at gripper assembly 32 and arrow 33 v represents the relative velocity vector at gripper assembly 33. In FIG. 4 a, scanner 36 b has detected the lead edge of the skewed carton blank 11 and the velocity vectors 32 v, 33 v are equal, i.e. no correction is being made yet.

In FIG. 4 b, an interval of time later, scanner 36 a has just detected the lead edge of carton blank 11 and velocity vectors 32 v and 33 v remain equal, i.e., no corrective action has been made yet, but the control system now has inputs from scanners 36 a and 36 b and calculates the desired corrective velocities and time intervals.

In FIG. 4 c, an additional interval of time later, the servo control system has commanded gripper assembly 33 to rotate faster, as represented by larger speed vector 33 v. The increased speed 33 v relative to speed 32 v causes the carton blank 11 to rotate counterclockwise relative to the plane viewed in FIGS. 4 a-4 c.

A commanded average speed increase at gripper assembly 33 during a programmed time interval (or number of encoder pulses), will cause a corresponding incremental realignment of the carton blank's leading edge. For example, if the control system detects the speed of the carton blank, e.g., 300 ft/min or 60 inches/second, and after evaluating scanner 36 a and 36 b signals triggered by the lead edge of the blank, determines that the edge passing under scanner 36 a is 2 milliseconds later than the edge passing under scanner 36 b, the control system calculates a speed adjustment and time duration factor, typically within preset parameter limits, to correct the 1 millisecond or 0.120″ alignment error (60 inches/sec×0.002 sec=0.120″). If the programmed speed increase of gripper assembly 33 was chosen at 2 inches/second (from 60 inches/second to an average of 62 inches/second) the increased speed would be required for 60 milliseconds (2 inches/sec×0.060 sec=0.120″). This presumes the use of a responsive servo system capable of rapid speed changes. The Vista window applicator regularly accelerates from 0 to 88 inches/second and back to zero in about 90 ms or about 2000 in/sec/sec. In comparison, the above correction move represents about 4000 in/sec/sec. However, the load inertia of the aligner gripper assembly 33 and opposing gripper assembly 34 is about 1/10^(th) that accelerated by the proven Vista applicator and within the capabilities of the servo system.

The speed increase is continued for an amount of time calculated by the control system sufficient to rotate carton blank 11 to the desired orientation, typically so that the leading edge of carton blank 11 is perpendicular to the folder/gluer's conveying direction D, as illustrated in FIG. 4 d. Then the velocity vectors 32 v and 33 v are once again made equal.

Scanners 36 a, 36 b are typically adjustable via sliding mounts that allow the scanners to be adjusted longitudinally (in the direction of motion of the carton blanks) or laterally (perpendicular to the direction of motion).

Longitudinal adjustment allows the two scanners 36 a, 36 b to sense the edge of two non-aligned edges simultaneously. For example, this latter scanner arrangement would be desirable when the carton blank 11 is not a simple rectangle, but rather has typical end flaps with varying lengths, or when it is desired to intentionally deliver carton blanks with the lead edge not square to the direction of motion, i.e., angled.

Lateral adjustment is desirable to accommodate varying carton shapes, especially cartons with die cut window openings, so that the gripper may grip along the length of a carton without interruptions while each scanner is laterally positioned to sense a desired lead feature of the carton blank.

If the scanners 36 a, 36 b are not in line with their respective grippers, the correction calculations are slightly more complicated, but are readily entered and accommodated via the graphical user interface and programming for the servo system. An illustration on the graphical user interface (such as a touchscreen) similar to FIG. 5 identifies the relative difference in positions of the gripper assemblies 32,33 and their respective scanners 36 a, 36 b and solicits an operator to enter measured values to define the offsets and gripper wheel spacing 53. The offsets 51, 52 and gripper assembly spacing 53 are used as initial inputs to the servo control system that are used along with carton speed and scanner 36 a, 36 b timing inputs to determine the appropriate adjustments in gripper assembly 33 speed applied adjustment and assembly duration. For a simplified system, scanner 36 b may be in a fixed, in-line relationship with gripper assembly 32 and scanner 36 a may be in a fixed, in-line relationship with gripper assemblies 33, 34 via mechanical mounts, or frames.

In other embodiments, the vacuum belt module 31 may be replaced by a roller or traditional folder/gluer carrier belt assembly in combination with gripper assembly 32 in known ways. Alternatively, gripper roller 32 may be driven by another servo motor (not shown), such as a counterpart to motor 33 m or by other types of motors suitable for providing a coordinated speed differential between gripper assembly 32 and gripper assembly 33. In another embodiment, a differential gear box may be provided between gripper assemblies 32 and 33 which can also provide a coordinated speed differential between gripper assemblies 32 and 33.

The foregoing disclosure provides a means of aligning, or squaring, the leading edge of a carton blank with the desired direction of conveying. It does not, however, provide a means for registering, or locating, a side edge of the carton-blank in the desired lateral position relative to the side frames of the carton folder/gluer so that a longitudinal fold will occur along a pre-scored line, or so that a window patch is applied square to the carton blank and in the desired lateral location on the carton blank.

It is also desirable to minimize the number of sensors needed to provide inputs to the squaring and lateral aligning process. This helps reduce the:

-   -   cost of the machinery;     -   complexity of the control programming by virtue of having fewer         inputs to react to; and     -   set-up preparation and adjustments required by the machine         operator.

The next described embodiment of the invention, which is illustrated schematically in FIG. 6, addresses the issues of squaring, lateral alignment, and a low sensor count. This embodiment requires only one servo axis to accomplish the squaring and aligning, similar to the servo arrangement disclosed in the squaring (only) embodiment.

In FIG. 6, a carton blank 11 is shown in its initial position, Pos. 1, and in a subsequent position, Pos. 2. In both positions, carton blank 11 is both out-of-square with the direction of conveying, D, and does not have its side edge E aligned with the desired lateral position illustrated as target line T. Gripper assembly 32 and gripper assembly 33 illustrated in FIG. 6 are similar to the previously described gripper assemblies illustrated in FIGS. 3 and 4 a-4 d. A scanner 36 b, similar to those in the previously described embodiment, is also incorporated in the instant embodiment. Scanner 36 b is used to sense the lead edge of carton blank 11 and to provide an input to the control system which notifies the control algorithm of the presence of a carton blank and to initiate the servo driven gripper assembly 33 corrective actions.

Signals from an additional scanner 37 are provided as inputs to the servo controller system. Scanner 37 is known in the art as an analog gap sensor consisting of a glass bifurcated light guide and an analog output photoelectric sensor, such as provided by Tri-Tronics® of Tampa, Fla. The analog gap sensor has a sensing zone 37 z up to about 1.5″ wide. A variable analog output, typically 0-10 volts, is governed by how much of the sensing zone is covered by the carton blank 11. Scanner 37 position is typically adjusted so that one-half of sensing zone 37 z is covered by the carton blank 11 when the carton blank edge E is in the desired lateral position relative to target line T. When one half of the sensing zone is covered, servo gripper assembly 33 is driven at a speed 33 v that matches the speed 32 v of gripper assembly 32.

Scanner 37 is shown in a location upstream, or behind, the rotational axis of the gripper assemblies 32, 33 to provide a means of sensing not only carton position, but also a means of sensing the correctional efforts of the servo driven gripper assembly 33 speed adjustments relative to gripper assembly 32. Scanner 37 could be located ahead of the grippers' rotational axes, but the controlling techniques would need to be effectively reversed from the detailed description that follows. The amount of offset OS could be varied by the designer, or user, as desired. However, the correctional algorithm would need parametric adjustments to obtain the desired corrective action.

In a further simplified embodiment, scanner 36 b could be eliminated by using scanner 37 to provide the initiation of the squaring and aligning operation as well as providing subsequent inputs to the controller for the squaring and alignment process.

In the case of FIG. 6, as the carton blank 11 is conveyed to an indicated first position, Pos. 1, the indicated angular misalignment will cause carton edge E to cover less than half of sensing zone 37 z. The servo control system processes this input and instructs servo driven gripper assembly 33 to slow down. The difference in rotational speed of gripper assemblies 32 and 33 is represented (not to scale) as speed vector 33 v 1 being less than speed vector 32 v 1. The amount of the speed decrease may be refined by using a PID (proportional, integral, derivative) control strategy such that if the amount of sensing zone 37 z covered becomes smaller and is growing smaller at an increasing rate, a more aggressive servo speed decrease command will be provided to gripper assembly 33, and vice versa, as is known in the art of servo control. This action will swing the carton blank in an incremental clockwise direction, CW1, until the sensor zone is again one-half covered, at which time 33 v will be readjusted to match 32 v.

FIG. 6 also represents the opposite carton blank 11 orientation, or a subsequent position, Pos. 2. In this case, more than half of sensor zone 37 z is covered and this input to the servo control system commands servo gripper assembly 33 to speed up causing counter clockwise rotation CCW2 which will cause the carton blank to rotate and decrease the coverage of sensor zone 37 z. The relative difference between the gripper speeds is shown with servo-driven gripper assembly 33 speed vector 33 v 2 larger than gripper assembly 32 speed vector 32 v 2

When these corrective actions are incremental and interposed within a short amount of time where 33 v is commanded to match 32 v, and if necessary, repeated, the carton edge E not only becomes parallel to target line T, but the carton edge also comes into lateral registration, or coincides, with the target line T.

This sequential positioning correction is illustrated in FIG. 7. Carton blank 11 is initially sensed in position 1. Scanning zone 37 z is not sufficiently covered by the carton blank 11 so the control system commands servo gripper assembly 33 to decrease in speed to pivot the carton blank in a clockwise manner as shown in the figure to initiate the lead edge squaring and side edge aligning process. Servo gripper 33 remains at reduced speed until approximately one half of scanning zone 37 z is covered by carton blank 11, or for a predetermined amount of time/distance according to a correction algorithm.

In pos. 2, the carton blank 11 has over-rotated as compared to Pos. 1. But this can be desirable in bringing the side edge E into the desired lateral position. In pos. 2, servo gripper assembly 33 is commanded to match the speed of gripper assembly 32. The matched speed mode may be for a predetermined amount of time/distance or it may instead rely on scanner 37 to indicate that carton edge has covered half, or more, of scanning zone 37 z. This has the effect of driving the carton slightly laterally to the right relative to gripper assemblies 32, 33. If the carton has become aligned, as sensed by a constant covered scanner sensing zone 37 z, then servo gripper assembly 33 continues to match gripper 32 assembly speed. If sensing zone 37 z becomes more than half covered, as shown in Pos. 3, gripper assembly 33 is commanded to exceed the speed of gripper assembly 32 and this has the effect of rotating the carton blank 11 counterclockwise until scanning zone 37 z is halfway covered again at which time gripper assembly 33 is commanded to again match gripper assembly 32 speed.

These corrective moves will continue until carton blank edge E is aligned with and parallel to target line T and scanning zone 37 z is one half covered by carton blank 11, at which time gripper assembly 32 and 33 speeds match and remain matched so long as one-half of scanner zone 37 z remains covered. Pos. 4 shows a subsequent position of carton blank 11, where it is aligned with and has one of its edges coincident with target line T as desired and no longer is under the influence of the aligning process for conveyance along a carton folder/gluer for further operations such as windowing, prebreaking, backfolding, and final folding.

In the foregoing discussion, a rectangular carton blank has been disclosed to simplify the description of the inventive method and apparatus. Typically, however, folding cartons, while often generally rectangular in shape, have many die cut facets and features that complicate the practice of the invention. FIG. 8 represents a basic folding carton blank 811, which includes notches and other contours that define flaps, tabs, and fold lines (also known as “scores”). These contours could confuse the control system unless provisions are made to exclude their effects on scanner 37 and the control system. In almost all cases, there is a substantially straight edge such as edge 811 a with a preceding flap 838 and trailing flap 839. Offsets 838 f and 839 f, corresponding to the length of the flaps, can be input in a conventional manner to the control system by the system operator via a graphical user interface (such as a touch screen). Thus, when flap 838 enters scanning zone 37 z, the control system will not begin to make corrections until the flap 838 has moved past scanner 37. Corrections may continue until flap 839 is expected to enter scanning zone 37 z and then the corrections are stopped.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the relevant arts that changes and modifications may be made without departing from the invention in its broader aspects. Therefore, the aim in the appended claims is to cover all such changes and modifications that fall within the true spirit and scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art. 

What is claimed is:
 1. A method for aligning a linear edge of a moving sheet-like article transverse to an intended direction of travel of the sheet-like article, said method comprising: positioning first and second drive mechanisms in contact with respective laterally spaced first and second sections of the sheet-like article for displacing the sheet-like article generally in the intended direction of travel, wherein said first and second sheet-like article sections are disposed along and include the linear edge of the sheet-like article; positioning first and second sensors in alignment with the first and second portions of the sheet-like article to respectively detect passage of the first portion of the linear edge past the first detector and passage of the second portion of the linear edge past the second detector for providing an output signal representing a difference in position relative to the intended direction of travel of the first and second portions of the sheet-like article; and coupling a controller to said first and second sensors and to at least one of said drive mechanisms, wherein said controller is responsive to said output signal for changing the speed of one of the first or second portions of the sheet-like article so that the first and second portions are aligned in the desired orientation relative to the intended direction of travel.
 2. The method of claim 1, wherein the step of providing an output signal representing a difference in position relative to the intended direction of travel of the first and second portions of the sheet-like article and includes the step of detecting a leading edge of each of the article's first and second portions, measuring a time interval between these two detections, and calculating a correction signal to bring the sheet's first and second portions in alignment transverse to the intended direction of travel, and providing said correction signal to one of said drive mechanisms.
 3. The method of claim 2 further comprising the step of equalizing the speeds of said first and second drive mechanisms and said first and second sheet portions following the aligning of said first and second sheet portions with each other.
 4. The method of claim 1 further comprising the step of compensating for nonlinear alignment of said first and second drive mechanisms and said first and second sensors in aligning the linear edge of the sheet-like article.
 5. The method of claim 1 further comprising the step of transporting the sheet-like article by means of upper and lower moving belts.
 6. The method of claim 1 further comprising the step of transporting the sheet-like article by means of a vacuum belt.
 7. A method for aligning a straight lateral edge of a moving sheet-like article having an intended direction of travel with a target line, said method comprising: positioning first and second drive mechanisms in alignment with respective first and second laterally spaced portions of the sheet-like article for engaging and displacing said first and second lateral spaced portions of the sheet-like article in the intended direction of travel; positioning a sensor adjacent to the sheet-like article's straight lateral edge for detecting the sheet-like article's straight lateral edge and a change in the extent of coverage of said sensor by the sheet-like article's straight lateral edge and for providing an output signal representing detection of said straight lateral edge and a change in the extent of coverage of said sensor by said straight lateral edge; and coupling a controller to said second drive mechanism and to said sensor, wherein said controller is responsive to said output signal for increasing or decreasing the speed of said second drive mechanism and the speed of the second portion of the sheet-like article relative to said first portion for positioning and maintaining said straight lateral edge in alignment with and parallel to the target line.
 8. The method of claim 7 further comprising the step of providing said sensor in the form of an analog gap sensor.
 9. The method of claim 8, wherein said analog gap sensor includes a glass bifurcated light guide and an analog output photoelectric sensor defining a sensing zone.
 10. The method of claim 9 further comprising the step of establishing alignment of the sheet-like article's straight lateral edge with said target line when the straight lateral edge covers approximately one-half of said sensing zone.
 11. The method of claim 7 further comprising the step of using a proportional, integral, derivative (PID) process for increasing or decreasing the speed of said second drive mechanism in proportion to the amount the lateral edge is not in alignment with the target line.
 12. The method of claim 7 further comprising the step of equalizing the speeds of said first and second drive mechanisms and said first and second sheet portions following the alignment of said first and second sheet portions with each other.
 13. A method for aligning or squaring a moving sheet-like article having at least one straight lateral edge with an intended direction of movement of the article, said method comprising the steps of: linearly displacing the article generally along the intended direction of movement by engaging and displacing first and second laterally spaced portions of the sheet; detecting the orientation of the article's straight lateral edge relative to the intended direction of movement; rotating the sheet-like article either clockwise or counter clockwise by changing the speed of the sheet's second portion relative to its first portion so as to re-orient the article's straight lateral edge in a pre-determined orientation relative to the intended direction of movement.
 14. The method of claim 13, wherein the pre-determined orientation of the article's straight lateral edge is parallel for aligning or perpendicular for squaring the straight lateral edge relative to the intended direction of movement of the article.
 15. The method of claim 13, wherein the article's intended direction of movement is defined by a linear target line, said method further comprising the step of detecting when said lateral edge and said linear target line are coincident and controlling the speed of the sheet's second portion relative to the first portion so as to maintain said linear target line coincident with said lateral edge.
 16. A method for aligning or squaring a straight lateral edge of a sheet-like article with an intended direction of travel of the article, said method comprising the steps of: linearly displacing the article generally along the intended direction of travel by engaging and displacing first and second laterally spaced portions of the sheet, including using respective first and second servo control systems for engaging and displacing said first and second portions of the sheet, respectively; detecting the orientation of the article's straight lateral edge relative to the intended direction of travel and outputting an analog control signal representing the orientation of said lateral edge relative to the intended direction of travel; and providing said analog control signal to one of said first or second servo control systems for changing the speed of said first or second portions of the article in re-orienting the article relative to the intended direction of travel and aligning or squaring the article's straight lateral edge relative to the intended direction of travel.
 17. Apparatus for aligning a moving sheet-like article with its intended direction of travel defined by a linear target line, said apparatus comprising: first and second laterally spaced drive mechanisms in alignment with one another in a direction generally transverse to the sheet-like article's target line, wherein said first and second drive mechanisms engage and linearly displace first and second laterally spaced portions of the sheet-like article in the intended direction of travel, and wherein said first drive mechanism is disposed between the target line and the second drive mechanism; a sensor disposed on the target line and adapted to detect a straight lateral edge of the moving sheet-like article and the angle between the sheet-like article's straight lateral edge and the target line direction of travel, wherein said sensor outputs a signal representing detection of said straight lateral edge and an angle between the target line and article's straight lateral edge; and control means coupled to said second drive mechanism and to said sensor, wherein said control means is responsive to said output signal and to the angle between the target line and the sheet-like article's straight lateral edge for decreasing the speed of said second drive mechanism and of the article's second portion when said straight lateral edge is disposed between the target line and said drive mechanisms and for increasing the speed of said second drive mechanism and of the article's second portion when said target line is disposed between said straight lateral line and said drive mechanisms. 